When micro-electro-mechanical systems (MEMS) devices such as MEMS inertial sensors are subject to external forces such as vibration, functionality may be lost and/or performance may be compromised. There have been various approaches to address how to reduce vibration of MEMS sensors.
In one prior approach, a comb drive was used to create an out-of-plane force to reduce vibration in a MEMS device. This approach is based on using a fringe field of the comb drive, which does not have a substrate beneath. Consequently, this approach is not usable for devices that do have electrodes beneath the comb drive (e.g., out-of-plane accelerometer and in-plane gyroscope). Moreover, the force produced is non-linear around zero deflection since it depends on displacement out-of-plane.
In another prior approach, a method for quadrature reduction in MEMS gyroscope devices uses a set of parallel plate electrodes to compensate for quadrature movement. However, using such electrodes to compensate motion out-of-plane results in a non-linear force, and if a DC bias is used, a change of resonant frequency. Moreover, a parallel plate actuator in unstable for higher actuation voltages.
While MEMS gyroscopes generally provide good angle random walk (ARW), robustness against severe shocks and vibration, and bias stability for certain applications, is inadequate. The reduction of bias can be achieved by improving the manufacturing process, by solving the problem at the system level, such as adding in-run calibration or by compensating the movement with electrostatic actuators. Nevertheless, the actuation in out-of-plane direction is more complicated as opposed to in-plane, since out-of-plane actuators based on parallel plate electrodes are inherently non-linear. Moreover, if single sided manufacturing technology is used, parallel plate force can act only in one direction. The in-plane actuation is less complicated due to the possibility to use drive combs which are linear actuators.
Accordingly, there is a need to actuate MEMS devices in an out-of-plane direction by a linear force, which is independent of both in-plane and out-of-plane displacement.